Heart rate variability (HRV) is a predictive indicator of survival after a heart attack. Over half a dozen prospective studies have shown that reduced HRV predicts sudden death in patients with MI, independent of other prognostic indicators such as ejection fraction. HRV refers to the extent of heart rate fluctuation and reflects the modulation of cardiac function by the autonomic nervous system and other physiological regulation systems. HRV analysis is a recognized tool for the estimation of cardiac autonomic modulation. More HRV means your heart is better able to adapt to changing circumstances. Less HRV means nerves and heart muscle cannot respond easily to change, potentially leading to out-of-rhythm beats or an abrupt, fatal stop. Less HRV appears to be a marker of fatal ventricular arrhythmia.
Stress may reduce HRV by affecting nerves that control the heart: The heart can be soothed and protected by stress reduction and exercise. Preliminary evidence suggests that both improve HRV. People can suffer from stress at work, at college, at home and virtually anywhere at anytime. It is well documented that stress not only affects one's immediate emotional state and mood, but also bodily functions in general. Stress and the stress hormone upset the autonomic systems of our body and endanger our health, in particular the health of our brain. Heart rate has been found to be a good indicator and quick signal of stress. The severity of stress can be expressed through changes in heart rate variability. This can damage brain cells, which will become more vulnerable to neurological insult, leading to brain ageing, stroke, and possibly Alzheimer's disease. There is a pressing need for strategies to reduce stress.
Baroreceptors situated in the aorta and internal carotid arteries play an important role in maintaining normal cardiovascular function and blood pressure. These receptors help to regulate our bodily functions by modulating cardiac function via autonomic and other physiological regulation systems. The rate and intensity of pressure signals at these receptors respond to our cardiac needs as a reaction to stressors experienced by the body. This response is exhibited in the form of blood pressure, heart rate changes and arousal of emotions. As bio-signals, such responses can be measured by changes in the is heart beat which are precisely represented by HRV using spectrum analysis.
Stress is different from anxiety due to the presence of an identifiable cause. Anxiety is a normal reaction to stress. However, the symptoms of anxiety and stress are driven by the same chemical reaction, with the same symptoms of a higher heart rate, sweaty palms and churning stomach. All these symptoms, and others, are explained by the physiological changes that occur when the mind and body experience stress or anxiety. The terms ‘anxiety’ and ‘stress’ are used interchangeably in the present application.